Int. J. Biol. Sci. 2013, Vol. 9 1013 Ivyspring International Publisher International Journal of Biological Sciences 2013; 9(10):1013-1020. doi: 10.7150/ijbs.7191 Review Roles of Eukaryotic Initiation Factor 5A2 in Human Cancer Feng-wei Wang1, Xin-yuan Guan2, Dan Xie1 1. Sun Yat-sen University Cancer Center; State Key Laboratory of Oncology in South China. Collaborative Innovation Center of Cancer Medicine. 2. Department of Clinical Oncology, the University of Hong Kong, Hong Kong, China. Corresponding author: Dan Xie, M.D. Ph.D. Sun Yat-Sen University Cancer Center, State key laboratory of oncology in South China, Collaborative Innovation Center of Cancer Medicine, No. 651, Dongfeng Road East, 510060 Guangzhou, China. Tel: 86-20-87343192 Fax: 86-20-87343170 Email: [email protected]. © Ivyspring International Publisher. This is an open-access article distributed under the terms of the Creative Commons License (http://creativecommons.org/ licenses/by-nc-nd/3.0/). Reproduction is permitted for personal, noncommercial use, provided that the article is in whole, unmodified, and properly cited. Received: 2013.07.18; Accepted: 2013.09.26; Published: 2013.10.12 Abstract Eukaryotic initiation factor 5A (eIF5A), the only known cellular protein containing the amino acid hypusine, is an essential component of translation elongation. eIF5A2, one of the two isoforms in the eIF5A family, is reported to be a novel oncogenic protein in many types of human cancer. Both in vitro and in vivo studies showed that eIF5A2 could initiate tumor formation, enhance cancer cell growth, and increase cancer cell motility and metastasis by inducing epithelial-mesenchymal transition. Accumulatied evidence suggests that eIF5A2 is a useful biomarker in the prediction of cancer prognoses and serves as an anticancer molecular target. In this review, we will focus on updating current knowledge of the EIF5A2 gene in human cancers. The molecular mechanisms of EIF5A2 related to tumorigenesis will also be discussed. Key words: Eukaryotic initiation factor 5A2, Cancer, Epithelial-mesenchymal transition, Metasta- sis. Introduction Amplification of 3q26.2 is one of the most fre- deoxyhypusine hydroxylase (DOHH) produces the quent genetic alternations found in solid tumors. In hypusine residue, a mature and active form of eIF5A 2000, our group isolated a putative oncogene, eukar- [6, 7]. Initially, eIF5A was thought to act in the final yotic translation initiation factor 5A2 (EIF5A2), from stage of the initiation phase of protein synthesis by 3q26.2, using the chromosome microdissection- hy- promoting the formation of the first peptide bond, brid selection technique [1]. In humans, eIF5A2 and its however, rencent reports have also suggested that isoform eIF5A1 are the only two eukaryotic proteins eIF5A participates in translation elongation [8, 9]. To that contain a unique hypusine residue [2, 3]. Hypu- date, two eIF5A isoforms have been identified and sine is a polyamine-derived amino acid that is gener- have been found to share about 80% of their cDNA ated in eIF5A by a post-translational enzymatic mod- sequences and 94% of their proteins. Both human ification that occurs in two steps. The first step in- eIF5A1 and eIF5A2 were shown to complement volves polyamine spermidine cleavage and the growth of eIF5A2 null yeast, indicating similar func- transfer of its 4-aminobutyl group to a specific lysine tions between the two human isoforms in terms of residue of the eIF5A precursor by deoxyhypusine eukaryotic cell survival [10, 11]. However, the genes synthase (DHS), thus forming a deoxyhypusine resi- encoding eIF5A1 and eIF5A2 are located on different due [4, 5]. Subsequent hydroxylation at carbon 2 of chromosomes. The EIF5A gene resides on 17p12-p13, the transferred 4-aminobutylmoiety intermediated by a genetically stable chromosome. eIF5A1 protein is http://www.ijbs.com Int. J. Biol. Sci. 2013, Vol. 9 1014 ubiquitously expressed in almost all cells and tissues ever the biological effects of eIF5A2 C-terminal region and plays crucial roles in translation elongation and remain unclear. As to the structure of eIF5A2, in brief, RNA metabolism [9]. In contrast, eIF5A2 expression is the N-terminal domain is dominated by β-strands and tissue and cell-type-specific, and is mainly found in the C-terminal domain consists of a three-turn α-helix testis, brain and several cancer cell lines and tissues α2 and five strands of β7-β11 [18]. [10]. Our previous studies showed that In addition to unique hypusine modification, over-expression of eIF5A2 could initiate tumor for- Ishfaq et al. find that both eIF5A isoforms are acety- mation, promote cancer cell growth and enhance cell lated at lysine-47, and hypusination of K50 can reduce invasion/metastasis by inducing epitheli- acetylation in eIF5A2. Moreover, both HDAC6 and al-mesenchymal transition (EMT) both in vitro and in SIRT were shown to deacetylate eIF5A2 in SW480 vivo, suggesting it might have an oncogenic role in cells when treated with three HDAC inhibitors, tri- mammals. In this article, we will focus on chostatin A (TSA), nicotinamide (NA), and SCOP402. EIF5A2-related studies that have been published over The authors further investigated the impact of the last ten years, particularly those articles pertaining hypusination and acetylation on the subcellular lo- to its modification, sub-cellular location, upstream calization of eIF5A2 via its expression of Flag-tagged regulation and roles in cancer cell proliferation, inva- eIF5A2 wild type and the mutants in Hela cells. The sion/metastasis, prognosis and prospects as a form of results showed that acetylation induced nuclear ac- cancer treatment. cumulation and hypusination induced cytoplasmice localization of eIF5A2 [20, 21]. Additionally, in 1995, Protein Modification and Sub-cellular Hannelore Klier et al. purified and characterized one Location major and three minor isoforms of human eIF5A from eIF5A2 is a small (approximately 17kDa) uni- Hela cells. The main form, which accounts for ap- versally conserved acidic protein classified in the eIF proximately 95% of all eIF5A, carries hypusine at po- family. The eIF family represents a group of proteins sition 50 and is amino-terminally acetylated as de- that are involved in the initiation step of the protein termined by amino acid composition analysis and translation. Each member of the eIF family plays a electrospray ionization mass spectrometry. In contrast unique role in the initiation process by interacting to the main form, all three minor isoforms of eIF5A with ribosomal subunits and mRNAs to form an are characterized by acetylation of lysine at position elongation competent complex [12]. With robust mo- 47. Furthermore, no phosphorylation was found in lecular genetics and biochemical studies, Saini et al. any of the purified human eIF5A isoforms [22]. With verify that eIF5A promotes translation elongation [9]. regards to the cellular location of eIF5A, Lipowsky et Different from other eIF members, eIF5A2 and its al. found that exportin 4 (Exp4 or XPO4) mediated the isoform eIF5A1 have a polyamine-derived amino ac- nuclear export of eIF5A1 by means of the trimetric id, hypusine, in their primary structures. Hypusine eIF5A1-Exp4-RanGTP complex, which required modification at the lysine-50 by DHS and DOHH is eIF5A1 hypusine modification [23]. In line with these mandatory for the maturation of eIF5A2 protein [11]. findings, Zender and colleagues identified that ex- Previous studies have shown that many kinds of cy- portin 4 (XPO4) was the nuclear export mediator of tokines and enzymes can enhance or decrease cell eIF5A2 in that nuclear accumulation of eIF5A1 or growth by regulating hypusine synthesis [13-17]. For eIF5A2 was found in XPO4 deficient cells [24]. Taken example, transglutaminases (TGase), calci- together, this evidence indicates that eIF5A2 is a um-dependent enzymes, can catalyze formation of a shuttling protein responsible for regulating genes’ cross-link between eIF5A hypusine residue and di- protein elongation in the cytoplasm (Fig 1.). Until methylcasein [13, 15]. However, the impacts of the now, eIF5A2 was still thought to be a cytoplasm pro- aforementioned cytokines and enzymes on eIF5A2 tein and no studies have shown that it can act as a warrants further investigation. The amino acid se- transcriptional factor in the nucleus. quences of the human eIF5A isoforms are conserved Upstream Regulation in the areas where hypusination takes place. The di- vergent residues between the human eIF5A1 and The EIF5A2 gene resides on chromosome 3q26, a eIF5A2 are mainly located on the C-terminal domain region that is frequently amplified in different human [18], suggesting that different functions between the malignancies, including pancreatic [25], esophageal two isoforms may be linked to the C-terminal domain. [26, 27], prostate [28], lung [29, 30], gastric [31, 32], The function of the C-terminal domain of eIF5A1 is ovarian [1, 33], colorectal [10, 34], liver [35], bladder shown by the finding that the mutation of Ser 149 to [36], breast [37], and nasopharyngeal carcinoma [38] Pro in yeast eIF5A1 decreases general protein synthe- (Table 1). However, over-expression of eIF5A2 pro- sis by 30% and increases mRNA stability [19]. How- tein does not always necessarily mean the amplifica- http://www.ijbs.com Int. J. Biol. Sci. 2013, Vol. 9 1015 tion of the gene. For instance, in the ovarian cancer open reading frames (ORFs) of the two isoforms were cell line UACC-1598, which has a high fold amplifica- expressed almost equally in 293T cells, suggesting tion of the EIF5A2 gene, the level of EIF5A2 mRNA is that the negative elements that inhibit the translation much higher than that of EIF5A, yet the amount of of EIF5A2 mRNA reside in the 5’-UTR or 3’-UTR. eIF5A2 protein is merely comparable to that of eIF5A1 Previous studies also showed that poly (A) tail length and no modified eIF5A2 is detectable in most cells played a critical role in regulating translation. Since (even when EIF5A2 mRNA is present) [11].